Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua


Our systematics research on the New Zealand land snail fauna combines morphological, molecular, ecology and geography to provide revisions, descriptions of newly discovered species, analyses of past and present distributions, and analyses of conservation priorities. We aim to supplement our publications in scientific journals with development of identification keys and fact sheets to assist biodiversity and biosecurity managers and members of the public.

New Zealand fauna globally significant – the conservation imperative

By global standards, New Zealand has an extraordinarily rich land snail fauna (with c. 1400 species), which, being highly distinctive in composition, represents a major contribution to global land snail diversity. All but five of the species are endemic to the New Zealand region (Barker 2005).

Internationally, land snails are recognised as highly vulnerable to anthropogenic disturbances and, sadly, are the taxonomic group with the highest recorded rate of extinction over the past millennium. New Zealand land snail species feature in the IUCN Red List and make up a significant component of the listed threatened animals in the New Zealand Threat Classification System (Hitchmough et al. 2007). Indeed, many New Zealand land snails are recognised as of high conservation concern and under active conservation management. Many other, mostly undescribed, are listed as ‘range restricted’ or ‘data deficient’ and proper systematic characterisation of these is urgently needed to guide conservation planning.

Relevance to biosecurity in New Zealand

Molluscs are a highly successful invertebrate group. In terrestrial environments the global diversity is in the order of 35 000 species. Among these there are a number of species that are being widely dispersed via human commerce, travel, and classical biological control, and include many recognised pest species. Thirty-one exotic species are already established in New Zealand and additional exotic species are not infrequently intercepted at our ports or managed as incursions.

There is increasing demand for improved biosecurity management. Molluscs are just one taxonomic group that are demanding the attentions of Biosecurity New Zealand, but are important in terms of (1) the magnitude of the global diversity, (2) the difficulties in identifications and recognition of biostatus, (3) several species are declared as unwanted organisms and thus specifically targeted by border management, and (4) the suite of invasive species, potentially of concern to New Zealand, continues to grow with changing patterns of trade and travel.

Invasive mollusc species are of significance to New Zealand with impacts on the indigenous flora (herbivory), indigenous fauna (predators; disease and parasite vectors) and agriculture/horticulture (herbivory; vectors of plant pathogens and animal parasite; contaminants of commodities).

Relevance to ecosystem management in New Zealand

Most of New Zealand terrestrial species are detritivores – in the order of 20 000 to 25 000 species of microbes and invertebrates that principally occur in the soil litter and A-horizons. These species are critical to decomposition processes that drive nutrient cycling and ecosystem function. Yet, currently, decisions about conservation management or resource use provide for little consideration of this major component of biodiversity. Land snails are numerically an important component of the New Zealand soil fauna, with high sympatric richness (20–80 species), abundance (up to 10 000 m2), and contributions to detritus turnover in indigenous ecosystems.

Biogeographic and evolutionary models

Terrestrialism in molluscs is ancient. The earliest fossils of terrestrial forms date from the mid-Paleozoic, and the adaptative radiation into the higher taxa (superfamily/family) that characterise modern faunas had occurred by the Lower Cretaceous (Solem & Yochelson 1979; Barker 2001). Their ancient origin and slow evolution at higher taxonomic levels, combined with low vagility, high rates of cladogenesis, and high rates of allopatric speciation (Solem 1984, 1990), make terrestrial molluscs superb biogeographic and evolutionary models.

Plesiomorphically, terrestrial molluscs possess a coiled shell within which the visceral organs are contained and into which the cephalic structures can be fully withdrawn for protection. While shell loss has occurred independently in a number of lineages, giving rise to the slug body form, in most regions the modern terrestrial mollusc faunas are dominated by animals that retain the external shell (snails). The shell is particularly useful in investigations of evolution, palaeoecology, archaeology and ecology, in being (1) species-specific yet malleable in both form and size by environment (e.g. Goodfriend 1986; Emberton 1994, 1995a; Chiba 1996) within measurable developmental constraints (e.g. Gould 1992); (2) with the individuals’ entire ontogeny conserved and displayed in the shell of the mature animal; and (3) at the faunal level, the range of shell morphologies is highly diagnostic of evolutionary ecology (Cain 1977, 1978a, b, 1981).

The New Zealand region represents an evolutionary hotspot for Mollusca, and understanding the New Zealand fauna will lead to major contributions to global understanding of evolutionary and biogeographic processes.

Land snails represent a highly distinctive element of the New Zealand invertebrate fauna. As patterns of diversity (e.g. regional endemism; hyperdiversity radiations) mirror those in other invertebrate groups, land snails represent useful models for biosystematic and ecological research.

New Zealand land snail communities are characterised by extremely high rates of alpha diversity (20–80 species per site cf. global norm of 5–10 per site). Understanding evolutionary and ecological processes shaping in these communities should make a major contribution to community assemblage ecology (Solem & Climo 1985; Barker & Mayhill 1998; Emberton 1995b; Barker 2005).